terraform-patterns

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• SKILL.md

SKILL.md (first lines)

# Terraform Patterns

Production Terraform patterns for maintainable infrastructure-as-code.

## Module Composition

```hcl
# modules/vpc/main.tf - Reusable VPC module
variable "name" {
  type        = string
  description = "VPC name prefix"
}

variable "cidr" {
  type    = string
  default = "10.0.0.0/16"
}

variable "azs" {
  type    = list(string)
  default = ["us-east-1a", "us-east-1b", "us-east-1c"]
}

resource "aws_vpc" "main" {
  cidr_block           = var.cidr
  enable_dns_hostnames = true
  enable_dns_support   = true

  tags = {
    Name        = var.name
    ManagedBy   = "terraform"
    Environment = terraform.workspace
  }
}

resource "aws_subnet" "private" {
  count             = length(var.azs)
  vpc_id            = aws_vpc.main.id
  cidr_block        = cidrsubnet(var.cidr, 8, count.index)
  availability_zone = var.azs[count.index]

  tags = {
    Name = "${var.name}-private-${var.azs[count.index]}"
    Tier = "private"
  }
}

output "vpc_id" {
  value = aws_vpc.main.id
}

output "private_subnet_ids" {
  value = aws_subnet.private[*.id]
}
```

## Root Module Composition

```hcl
# environments/production/main.tf
terraform {
  required_version = ">= 1.5.0"

  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"    # Pin major version, allow minor updates
    }
  }

  backend "s3" {
    bucket         = "mycompany-terraform-state"
    key            = "production/terraform.tfstate"
    region         = "us-east-1"
    dynamodb_table = "terraform-locks"    # State locking
    encrypt        = true
  }
}

module "vpc" {
  source = "../../modules/vpc"
  name   = "prod"
  cidr   = "10.0.0.0/16"
  azs    = ["us-east-1a", "us-east-1b", "us-east-1c"]
}

module "database" {
  source    = "../../modules/rds"
  vpc_id    = module.vpc.vpc_id
  subnet_ids = module.vpc.private_subnet_ids

  instance_class    = "db.r6g.xlarge"
  allocated_storage = 100
  multi_az          = true
}

module "app" {
  source     = "../../modules/ecs-service"
  vpc_id     = module.vpc.vpc_id
  subnet_ids = module.vpc.private_subnet_ids

  container_image = "myapp:${var.app_version}"
  desired_count   = 3
  cpu             = 512
  memory          = 1024

  environment_variables = {
    DATABASE_URL = module.database.connection_string
    LOG_LEVEL    = "info"
  }
}
```

## State Management

```hcl
# Remote state data source: reference other state files safely
data "terraform_remote_state" "networking" {
  backend = "s3"

From vibeeval/vibecosystem, MIT.

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